24 Feb 2014: Analysis

Is Weird Winter Weather Related to Climate Change?

Scientists are trying to understand if the unusual weather in the Northern Hemisphere this winter — from record heat in Alaska to unprecedented flooding in Britain — is linked to climate change. One thing seems clear: Shifts in the jet stream play a key role and could become even more disruptive as the world warms.

by fred pearce

This winter’s weather has been weird across much of the Northern Hemisphere. Record storms in Europe; record drought in California; record heat in parts of the Arctic, including Alaska and parts of Scandinavia; but record freezes too, as polar air blew south over Canada and the U.S., causing near-record ice cover on the Great Lakes, sending the mercury as low as minus 50 degrees Celsius in Minnesota, and bringing sharp chills to Texas.

Everyone is blaming the jet stream, which drives most weather in mid-latitudes. That would be a significant development. For what happens

NASA Goddard Space Flight Center

The polar jet stream may be driving a "hemispheric pattern of severe weather."

to the jet stream in the coming decades looks likely to be the key link between the abstractions of climate change and real weather we all experience. So, is our recent strange weather a sign of things to come? Are we, as British opposition leader Ed Milliband put it this month while surveying a flooded nation, "sleepwalking to a climate crisis"?

The story gets tangled because trying to identify long-term trends amid the noise of daily weather is hard.

The U.K. Met Office, which keeps a global weather watch, said in a rush report put out in mid-February that we are experiencing a "hemispheric pattern of severe weather," and that the events are linked. The most extreme days of the U.S. cold event, for instance, coincided with some of the most intense storms over the U.K. And physically the connection is through the polar jet stream, which the report said showed a "persistent pattern of perturbations" — in other words, it ran wild.

The polar jet stream is a narrow stream of fast wind circling the globe from west to east at the top of the troposphere from 7 to 12 kilometers up, and usually between 50 and 70 degrees north. It forms where cold, dense air from the Arctic meets warmer and less dense air from mid-latitudes. At the

boundary, winds rush in to equalize the pressure difference. The earth's rotation diverts these winds to travel eastward.

As the jet roars around the world, it drags weather systems with it. Most of Europe's weather rides in under the jet stream from the Atlantic, and most of the western U.S.'s weather comes from the Pacific in a similar manner.

This year, the jet has been unusually far north in the Pacific, bringing balmy weather to Alaska. But across the Atlantic it has been unusually far south, unusually persistent, and 30 percent faster than normal. It has sent more than 30 storms, many of them much larger and more intense than normal, crashing into the shores of Britain in the past three months. With the storms have come high winds and heavy rains almost every day, delivering amounts of precipitation unseen in records going back more than a century — and probably exceeding anything else in the last 250 years, according to the Met Office report.

At the annual meeting of the American Association for the Advancement of Science in Chicago this month, climatologist Jennifer Francis of Rutgers University linked "this bizarre winter" to climate change, and in particular to changes in the jet stream caused by a warming Arctic. "Weather patterns are changing," she said. "We can expect more of the same."

Francis notes that the Arctic has been warming faster than the rest of the planet in recent decades, driven by melting ice that replaced reflective white surfaces with dark, energy-absorbing ocean. That is expected to continue. While lower latitudes will also warm, the result will be to reduce the temperature gradient between polar and mid-latitude air that drives the jet. So, says Francis, we can expect the jet to slow. A slower jet is generally more meandering and inclined to get "stuck," delivering unchanging weather.

There is one problem with this analysis as regards recent events, says Tim Woollings, who researches atmospheric dynamics at Oxford University in England. While the jet stream has indeed been "stuck" for the past two months, delivering cold weather to North America and storms across the Atlantic, it is not slow and meandering. Across the Atlantic at least, it has been fast and remarkably straight. "That is the exact opposite to the weak meandering jet of your hypothesis," Woollings told Francis in an email exchange last week that both shared with Yale Environment 360.

That certainly doesn’t prove Francis wrong. Woollings agrees that Francis’s prediction of a stuck meandering jet looks very like the situation in the Pacific this winter. But it does complicate claims that this winter’s

Britain’s Met Office says the real driver of recent climate patterns has been the jet stream over the Pacific Ocean.

extremes can be blamed on man-made climate change.

So what is going on? The Met Office came to the conclusion that the real driver of the action in recent months was not in the Arctic or the Atlantic, but far away in the western Pacific Ocean. The jet stream, remember, is a global wind, circling the earth. This winter, the jet stream over the Pacific has been deflected much further north than usual. This, according to the Met Office, is likely a consequence of some combination of heavy rains over Indonesia, warm Pacific waters, and unusual pressure systems.

The displaced Pacific leg of the jet stream dragged warm air up over Alaska. But, once east of the Rockies, it met the dense cold air of the Arctic and plunged south. A long way south — as far as Texas at times. This southward excursion of the jet brought freezing weather across much of the U.S. But it also brought that cold polar air into contact with warm southerly breezes. Thus the temperature gradient at the boundary between polar and non-polar air was exceptionally great. At times, says Francis, Arctic air was meeting tropical air as the polar jet coalesced with the sub-tropical jet, which forms where tropical air meets air from the north.

The scientists agree that this exceptional temperature difference dramatically speeded up the jet stream as it pushed out over the Atlantic on its unusually southerly trajectory. A fast jet stream is usually also a straight jet stream. And the southerly route allowed the surface air it pulled along to pick up unusual amounts of moisture evaporating from the warm waters of the Atlantic.

The result was that the jet slammed a long succession of intense storms into southern England, where they would normally hit Scotland or miss the U.K. altogether. The storms contained huge volumes of moisture. And, to add to the tumult, the fast winds across the Atlantic also whipped up big waves and tidal surges; so in places record flood flows coming down rivers met flood waters coming off the sea. Parts of Britain were submerged.

Where does this leave us on climate change? It is no great surprise that there is confusion. Weather is weather. It is always changeable, with a large

Scientists remain uncertain about how the major features of world’s weather will respond to global warming.

random element. Stuff happens. The Met Office notes that the winter’s weird weather has a range of causes besides the jet stream, including unusual upper atmosphere winds over the North Pole, and anomalies in the eastern Pacific that have delivered severe drought to California. There is, the Met Office says, no compelling evidence from this winter to suggest that there is a new emerging pattern.

But that doesn’t mean nothing is going on. Long-term trends are hard to spot, and natural variability is still generally dominant over the subtle changes in climate, or "average weather."

Yet there are some instances where attribution is possible. For example, climate researchers have persuasively argued that a few intense heat waves — such as the one that killed 70,000 people in western Europe in 2003 — would have been highly unlikely without the added impetus of global warming. But for weather extremes other than rising temperatures, unambiguous attribution of even extreme events is very hard to make, whatever the suspicions that something is up.

Climate scientists remain very uncertain about how most of the major features of the world’s weather will respond to global warming. The climate will change, for sure, but exactly how is a tough call.

El Niño, the Asian and African monsoons, Atlantic hurricanes, the jet streams: The most recent report of the Intergovernmental Panel on Climate Change (IPCC), issued last October, puts a big question mark over the likely trends for all of them. And while Francis suggests the polar jet stream should slow as the Arctic warms, the IPCC noted that most climate models predict a faster polar jet.

Actual trends so far don’t tell us much. According to the Met Office, the number of storms crossing the Atlantic in a normal year is no higher today

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than 150 years ago. But Xiaolan Wang of Environment Canada, a government agency, last year reported evidence that winter storms are becoming stronger over the North Atlantic. This may not have anything to do with the jet stream, however. These storms could just be picking up more moisture from an Atlantic that is now substantially warmer than in past decades.

Data from weather stations around the world reveal more extreme precipitation events — and more droughts, too. This is firmly in line with the predictions of climate models and is "what is expected from fundamental physics," says the Met Office. A warmer atmosphere will contain more energy, and more moisture from evaporation, says Woollings. It already does. And, in general, more energy and moisture will mean wetter storms in many places.

Weird weather is definitely on the agenda, and the jet stream is very likely to be an important part of it. The nightmare scenario is that Francis will be proved right about the jet stream becoming more "stuck" in a particular trajectory, but that, as happened this winter, it will get stuck while traveling at express speed and bringing strong winds and heavy rain with it. The Met Office says the Francis scenario "raises the possibility that disruption of our usual weather patterns may be how climate change may manifest itself." If so, that would indeed unleash the perfect storm.

COMMENTS

Much of what is going on here is based on solid physical laws. We know global warming is real because we know that greenhouse gases such as CO2, water vapor, and methane absorb and reflect infrared light, and more gasses=more heat.

Similarly, we know that darker colored open water in the Arctic will absorb more light and heat than lighter colored ice packs, and it too will accelerate global warming.

My question here is whether Jennifer Francis' claims that the temperature gradient between mid and polar latitudes dictates the speed of the jet stream and that a slower jet will meander and get stuck, are similarly based on solid physical laws or not?

Posted by
Adam Albright
on 25 Feb 2014

The distribution of energy about the globe by ocean currents and winds is extremely complex if not simply chaotic. The answer lies not in analysis of climate measurements but in an appreciation of the fundamental underlying physics, starting with the concept of conservation of energy.

The earth absorbs energy from daylight and re-radiates it into space at night. Water vapor, dust particles and gases in the atmosphere moderate this energy flow to maintain the range of temperatures at which life on earth is possible.

Mankind is the only life-form that requires more than its food to meet its energy needs. Over the last century we have increasingly relied upon electricity to meet this need but we have produced it by grossly inefficient means.

Nuclear and coal fired power stations are no more than 40 percent thermally efficient while gas plants achieve only 50 percent. Add to this the energy losses from poorly insulated buildings and you get at least two units of energy being injected into the climate for every one unit of electricity delivered to the grid. This happens continuously, there are no compensatory losses, the earth's natural heating/cooling cycle is unbalanced and energy builds up in the atmosphere.

While we continue to pump energy into the atmosphere we must expect the atmosphere to deliver us a violent climate.

Posted by
IanS
on 25 Feb 2014

I would like to make a few minor but important corrections to this post:

1) This winter's pattern cannot be related directly to climate change nor, in particular, to rapid Arctic warming, but it is an example of the very amplified (wavy) jet stream pattern that I would expect to occur more often as greenhouse gas emissions continue to rise.

2) Our research suggests that rapid Arctic warming and a smaller Arctic/mid-latitude temperature difference will result in a slowing of the west-to-east winds of the jet stream only, not the overall wind speed of the jet stream.

3) The persistent jet-stream pattern in the Atlantic this winter is not inconsistent with our theory. While the west-to-east winds there were stronger than normal, it is the persistence of the overall, northern-hemisphere pattern that created the record flooding in the UK. Over the Pacific and North America, the westerly winds were weaker than normal. An increased persistence of jet-stream configurations is what I would expect to occur in the future.

Posted by
Jennifer Francis
on 25 Feb 2014

Carbon dioxide is not a 'greenhouse gas." CO2 is in perfect equilibrium in the environment. Neither fossil fuels use nor carbon dioxide affect climate. A high-school sophomore can compute a mass balance for carbon dioxide using public information sources. Do your homework!

Anthropogenic global warming is a textbook mania, based on falsehoods. The media feed the mania by fomenting panic. We can use as much fossil fuels as we please without having any effect on climate. Regulating or limiting human CO2 emissions is a colossal waste of money and effort.

Carbon dioxide has no adverse effect on climate. Changes in ambient CO2 result from natural temperature changes caused by other forces. A warmer temperature results in a higher equilibrium CO2 content. Cooler weather means less ambient CO2.

96.8% of CO2 emissions are from natural sources. The earth reabsorbs 99.9985% of CO2 emitted from all natural and human sources. The average residence time of CO2 in the atmosphere is less than 11 minutes. It goes into seawater, where it is quickly converted to carbonate rock, where it will remain for tens of millions of years.

Limestone, for example = CaCO3. An acre of oysters or coral can form more than ten tons of carbonate rock in a single growing season. The carbonate formation process is voracious and robust, and will consume all the carbon dioxide that humans can generate.

Posted by
Miner49er
on 25 Feb 2014

Having stumbled on a place where science is valued over political consideration, I'm hoping I might receive answers to a few questions which seem to be beyond the mainstream media to answer. The main one is regarding the question of whether jet streams require warming or cooling to push them to new speeds. Since the standard behavior for streams is typified by slower speeds in summer and faster speeds in winter, surely the recent behavior of the northern, polar jet stream over the Atlantic Ocean indicates it's currently receiving a more intense form of cold air than usual to fuel the mixture? Could the Pacific's undulations, which suck in both hotter and colder air from more diverse latitudes, followed by the current cold over the US be combining to create a fast, straight effect over the Atlantic? Secondly, regarding the undulating behavior which has been developing globally since 2009, as jet streams are a constant battle between equatorial and polar air masses doesn't this indicate that the struggle is intensifying rather than dying out? In the same way equatorial heat surges through temperate regions in undulating patterns during periods of global warming, any resurgence of polar power would surely manifest through the type of behavior we’re seeing presently like a metaphorical stone dropped into the biosphere's pond? To quote CERN physicist Brian Cox in one of his recent BBC TV shows, "... the physics of the universe are the same as the physics of the kitchen," a statement which implies the underlying cause behind climatic extremities is analogous to placing a glass of boiling hot water into the icebox, rather than the refrigerator.

Posted by
Richard Moseley
on 25 Feb 2014

IanS is wrong that the inefficiencies of our machines appreciably warm the earth by directly adding energy to the atmosphere. This effect is tiny, and the amount of energy is very small in proportion to the solar energy coming in.

(And is also small in comparison to the heat radiated from the earth itself, left over from its gravitational formation, and from nuclear decay of uranium and from tidal forces, as well as the heat generated by the chemical reactions of life.)

The atmosphere is largely transparent to heat, and it is greenhouse gases that are responsible for what little it does trap. Adding more ghgs to the atmosphere results in the atmosphere being able to absorb more heat, raising its temperature. Most of that heat will come from the sun, since it is the overwhelmingly largest contributor of energy at the earth's surface and atmosphere.

Posted by
crf
on 26 Feb 2014

Decided to take up Miner49ers challenge and do my homework. This is what I found on the CO2 Science website:

"CO2, is nearly transparent to the solar radiation emitted from the sun, but partially opaque to the thermal radiation emitted by the earth. As such, it allows incoming solar radiation from the sun to pass through it and warm the earth's surface. The earth's surface, in turn, emitts a portion of this energy upwards toward space as longer wavelength or thermal radiation. Some of this thermal radiation is absorbed and re-radiated by the atmosphere's CO2 molecules back toward earth's surface, providing an additional source of heat energy. Without water vapor, CO2, and other radiatively-active trace gases in the air, the planet's average temperature would be about 34°C cooler than it is at present." So, perhaps CO2 is a greenhouse gas after all.

Also, I note that the portion of CO2 in the atmosphere has grown from 320ppm to 400ppm over the past 50 years with no obvious natural process evident that would drive that change, so perhaps the burning of fossil fuels do play a part in that shift.

Posted by
Adam Albright
on 26 Feb 2014

"Scientists remain uncertain about how the major features of world's weather will respond to global warming." But there is no global warming!

Posted by
Alec
on 26 Feb 2014

I agree with crf that machine losses are insignificant but that was not my point.

Theoretical physicist Alfred Betz calculated that the maximum energy a perfect machine can extract from a fluid flow is 59% of the energy at the input. Today a modern wind turbine can extract over 50% of the energy in the wind but it is impossible to produce one which will reach or exceed 59%.

Thermal systems require a similar flow of energy in the form of heat from a high temperature source, such as a furnace or nuclear pile, flowing to a low temperature sump, the atmosphere. In thermal systems the nearest equivalent to Betz's limit is defined by the Carnot cycle. In practice thermal efficiencies way below 50% are common and higher levels rarely achieved, no matter how efficient the machines. The key point is that the laws of physics limit the energy that can be extracted. In the case of thermal systems the waste heat is lost into the atmosphere. For wind turbines the unused energy remains in the wind.

At the very least this waste energy in the form of heat is equivalent to, and probably twice as much as, the total electrical energy from thermal generation across the globe. That is not a small number and one easily capable of tipping the global heating/cooling balance.

Posted by
IanS
on 27 Feb 2014

My mathematician friend told me many years ago that a professor of math in his department studied the phenomenon of global warming while her daughter studied meteorology, ultimately getting a doctorate and tenure-track position at a prestigious American university. I distinctly remember my friend's words: Weather systems will become stuck, persistent, stagnant, stalled, etc., everything we have experienced in the northern hemisphere this winter. I had this letter published in the Syracuse, NY, Post-Standard on May 2, 2011:

To the Editor:
One of the many consequences of global warming is stalled weather systems. Don’t let the weather man fool you into thinking it’s just Mother Nature.

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